When Apple reveals iCloud at WWDC on Monday, it’ll have the kind of impact the iPod has had, predicts Kevin Fox, a Silicon Valley software veteran who’s worked at Apple, Yahoo and Google.
“The rumblings are huge,” says Fox, lead designer at Mozilla. Fox worked on Newton software before designing Yahoo’s chat service and then software for Google (including Gmail 1.0, Google Calendar 1.0, and Google Reader 2.0). He continues:

WWDC 2011 Prelude

WHAT I KNOW

If I were to publish everything I know regarding tomorrow’s announcements, it would be a short and decidedly unsensational article. What I know are a handful of minor features at the edges. The big picture regarding iOS 5 and iCloud — and how the two interrelate — is an utter mystery to me. These things have been as well-kept secrets as any major projects from Apple in recent years.
iCloud’s expected music storage has of course leaked, but that’s almost certainly the inevitable result of Apple’s dealings with the music labels. Music storage is a feature of iCloud; iCloud is not a music service.

WHAT I’VE HEARD, AND BELIEVE, BUT BY NO MEANS KNOW AS FACT

The italicized sentence that follows is fourth-hand information, at best, and also the sort of thing that many of you might have already guessed based merely on your own hunches and hopes. But here goes:
Don’t think of iCloud as the new MobileMe; think of iCloud as the new iTunes.
Syncing data between devices tends to work best when there’s a canonical store. I.e. with Dropbox, you might have three, four, five devices syncing data on the same account. The canonical central store, however, is Dropbox’s cloud-based server. With iPhones, iPods, and iPads, the central store for almost all data stored on the devices is iTunes running on your Mac or PC.
With iCloud, that should shift to the cloud. iTunes, the desktop app, currently syncs the following things with iOS devices: audio, movies and TV shows, iBooks e-books, App Store apps, contacts, calendars, bookmarks, notes, and any sort of files shared between iOS apps. All of these things would be better served syncing over-the-air via the so-called cloud.
Gruber continues on, and you really should go read his entire piece, but I think the most important parts of what he wrote are quoted above.
For what it's worth, I'll give my opinions, which are by no means backed by any sources of my own. In no particular order:
1. I think OS X Lion GM seed will be released to developers. It will be released as soon as June 14th but no later than June 28 to the public.
2. iOS 5 Developer Preview 1 will be released to developers.
3. I could maybe see iCloud DP1 being made available but has Apple ever released a developer preview of a web based app before other than the beta versions of Mobile Me Calendar & Mail last summer? Those didn't have APIs associated with them though. It seems like me they would need to preview them if they wanted developers to build them into their apps and test them though. This one is a big maybe.
4. Some sort of Twitter integration with iOS 5. Not sure if it will be a very simple share-your-photo-on-twitter menu item on the Send Menu in the Photos app or what. It could be "huge" as Scoble says.
5. iOS 5 / Lion / iCloud integration. Deep. I think iCloud needs to have this to avoid become just another Mobile Me iteration.
6. No hardware (of course). Just wanted to remind anyone who hasn't gotten the memo yet.
7. I have a hard time believing any of the Time Capsule related rumors. By locking iCloud into Time Capsule I feel Apple would be making a big mistake. I truly hope this is not the case.
8. iCloud will have some sort of streaming music component.
9. iOS 5 will have a revamped notifications system. I feel there will be much disappointment if it doesn't. I think Apple is well aware of this.
10. Improved interface for accessing, organizing, and viewing apps in iOS 5. Gruber makes a very good point. Folders helped alleviate this pain but it was akin to putting a bandaid on a compound fracture. Power users need a better solution and considering just how many apps are downloaded by all iOS users, not just the geeks are power users these days.
I'm sure there will be much more news tomorrow than these 10 points I have listed here, but these 10 items are the ones I feel most confident about. Numbers 3, 7, and 10 are the ones I doubt the most, but I left them in there anyway.